Bonded part and method for producing same

ABSTRACT

A bonded part such as a rubber to metal bonded part and process for producing a bonded part including a rubber and metal part, and particularly for producing an automotive torsional vibration damper, comprising the steps of placing uncured elastomer composition comprising an elastomer, at least one curative, and preferably, at least one rubber-to-metal adhesive adjuvant into a shape-forming mold, and curing the elastomer in two stages, wherein in the first curing stage the elastomer composition is less than fully cured and in the second curing stage, preferably performed with the elastomer composition in contact with a metal surface of the rubber and metal part, the elastomer composition is at least substantially fully cured. According to one embodiment, the present invention allows for the elimination of the step of applying an adhesive to the metal surface prior to application of the elastomer composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/081,464filed Feb. 2, 2002, which claims the benefit of priority of U.S.Provisional Patent Application No. 60/271,579, filed Feb. 23, 2001.

BACKGROUND OF THE INVENTION

The present invention relates to a bonded part comprising a rubbermember bonded to a second substrate, and to a rubber-to-metal bondedpart, and to a torsional vibration damper, and to a process for directlybonding rubber to at least a second substrate which may be a metalsubstrate, and to a method of bonding an intervening rubber member,which may optionally be applied under compression, between two metalmembers, such as in the manufacture of crankshaft torsional vibrationdampers.

High strength bonding of rubber to substrates and particularly to metalsubstrates is desirable for numerous applications, including in themanufacture of rubber composite articles characterized by high and/ordynamic loading or extreme environmental conditions, e.g., tires, belts,rolls, seals and hose; and in those applications involving or callingfor some level of vibration isolation and/or shock damping, e.g.vibration isolators such as engine mounts, vibration isolation mounts,vibration dampers, couplings, suspension bushings and transmission andaxle seals.

A wide variety of methods have historically been employed to address oneor another aspect of rubber-to-metal bonding, including improvingadhesive strength, controlling the rubber compression or shrinkage leveland/or increasing production efficiency, etc. In general, particularlyin the area of vibration isolators and/or shock dampers, wherein anannular cured rubber member is disposed or sandwiched between two outermetal substrates, a limited level of mechanical bonding can be achievedby compressing the rubber member between outer metal members and relyingon frictional forces between the rubber and metal surfaces. Highstrength rubber-to-metal bonding however is generally achieved throughadhesive bonding of the fully vulcanized rubber member placed betweenthe outer metal members through the action of one or more adhesivesapplied at the rubber-to-metal interface (hereafter, “post-vulcanizationbonding”). An advantage of post-vulcanization bonding in theconstruction of parts wherein a rubber member is disposed between twoouter metal surfaces is that since the rubber member is fully curedprior to its placement between the metal surfaces, it does not exhibitsignificant shrinkage and thereby resides under tension between themetal surfaces upon exposure to temperatures below its vulcanizationtemperature.

Alternatively, un-cured elastomeric material is introduced between theouter metal members to which a rubber-to-metal adhesive has beenapplied, and the elastomeric material is then fully cured in contactwith the adhesive-coated metal substrate (hereafter, “vulcanizationbonding”). A high degree of process control is required in the practiceof this method in order to provide a homogeneous and consistent product.Moreover, dampers must be assembled relatively quickly after rubbermixing according to this method, which reduces production flexibility,and therefore, production efficiency. An additional disadvantage ofconventional vulcanization bonding techniques in the construction ofparts wherein a rubber member is disposed between two outer metalsubstrates is that since the rubber member is fully cured while incontact with each of the metal surfaces, it tends to exhibit at leastsome degree of shrinkage after curing, and thus resides under tensionbetween the metal surfaces almost immediately as the exposuretemperature falls below the vulcanization temperature, with adverseimpact on the durability of the article.

In both of these methods, compression forces have also optionally beenapplied to provide further stabilization of rubber-to-metal engagementor to eliminate the tension resulting from shrinkage of the rubber.

In general, in each of the three conventional methods of press moldingrubber or rubber-to-metal bonded assemblies exemplified by crankshafttorsional vibration dampers according to either vulcanization- orpost-vulcanization bonding techniques, i.e., compression molding,transfer molding and injection molding, the problems associated withrubber-to-metal adhesives applied at the rubber-to-metal interface areessentially the same. First is the environmental concern; most suchadhesives contain toxic constituents and are thus difficult and costlyto handle, to store and to dispose of. Prior to the application of therubber-to-metal adhesive, the relevant metal surface must moreovergenerally undergo intensive surface cleaning and preparation to ensureadequate bond strength. Furthermore, due to their typically volatilenature, the rubber-to-metal adhesive composition may sublimate orvolatilize at vulcanization temperatures prior to the point at whichadequate contact between the metal and the rubber is achieved, therebydecreasing the adhesive's efficiency, potentially causing fumes at thepress and/or resulting in mold fouling. In addition, in vulcanizationbonding processes there is the problem of “mold sweeping”, whereby asmolten rubber enters the mold cavities prior to curing, it flows acrossthe adhesive-coated metal, tending to sweep along with it at least aportion of the adhesive, thus further reducing its efficiency.

U.S. Pat. No. 4,889,578 to Kei et al. describes a process for making arubber vibration insulator including the steps of adhering, byvulcanization in combination with a metal adhesive at therubber-to-metal interface, an un-vulcanized rubber layer to the outersurface of an inner metal fitting; adhering by vulcanization incombination with a metal adhesive at the other rubber-to-metalinterface, another un-vulcanized rubber layer to the inner surface of anouter shell metal fitting; applying a halogen compound solution to theopposite, non-bonded surfaces of both of the rubber layers;press-fitting the inner metal fitting having the rubber layer to theouter shell metal fitting having the rubber layer such that the tworubber layers form a rubber-to-rubber interface, using a lubricant or alubricating adhesive, and effecting adhesion between the vulcanizedrubber layers through heating the above described mutually fittedbodies.

This process presents several drawbacks. In particular, the utilizationof a halogen compound e.g., chlorinated or brominated polymers andsodium hypochlorite, or chlorinated cyanuric acid solution as apretreatment agent, is still required to bond the adjacent vulcanizedrubber surfaces. Moreover, the process is characterized by a pluralityof labor steps; each of which introduces incremental cost increase tothe process. In addition, the process relies nonetheless on theutilization of a rubber-to-metal adhesive on the metal surface prior toapplication of the rubber thereto in order to achieve satisfactoryadhesion of the rubber to the metal.

SUMMARY OF THE INVENTION

The present invention provides a bonded article, comprising at least acured rubber member disposed between a first outer member and a secondouter member, wherein the rubber member is the reaction product of atleast one elastomer, at least one adhesive adjuvant and at least onecurative, and the rubber member is formed and arranged to reside betweenthe outer members in at least one of a neutral state and a state ofcompression at a temperature in the range of from about −20° C. to about120° C.

In a further embodiment, the present invention provides a method ofproducing a bonded part comprising a cured rubber member disposedbetween a first outer member and a second outer member. The methodcomprises the steps of placing an uncured elastomer compositioncomprising an elastomer, at least one curative and at least one adhesiveadjuvant into a shape-forming mold, and curing the composition in atleast two stages, wherein in a first curing stage the composition isless than fully cured and in a second curing stage, preferably performedwith the partially cured elastomer composition in contact with at leastone outer member surface, the elastomer composition is at leastsubstantially fully cured.

According to one embodiment, the present invention allows for theelimination of the step of applying one or more adhesives to the outermember surface at the relevant interface prior to introduction of theelastomer composition.

In a further embodiment, the uncured elastomer composition comprises atleast two curatives, each of which is characterized by distinct cureactivation conditions, including temperature, exposure period andpressure. According to this embodiment, the first curing step ispreferably performed in a shape-forming mold, by adjusting at least oneof a first temperature, a first applied pressure and a first exposureperiod, in such a manner as to activate the first curative to a pointwherein the elastomer composition is partially cured; and thereafter thesecond curing step is performed with the elastomer composition incontact with the outer member surface, optionally under compression ofup to about 50%, through adjusting at least one of a second temperature,a second applied pressure and a second exposure period, in such a manneras to activate the second curative to a point wherein the elastomercomposition is at least substantially fully cured.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will becomeapparent from the following description and accompanying drawings, inwhich like reference numerals denote like parts, and:

FIG. 1 is a perspective, partial cut-away view of a crankshaft torsionalvibration damper made in accordance with an embodiment of the presentinvention;

FIG. 2 is a perspective, partial cut-away view of a crankshaft torsionalvibration damper made in accordance with another embodiment of thepresent invention;

FIG. 3 is a perspective, partial cut-away view of a crankshaft torsionalvibration damper made in accordance with another embodiment of thepresent invention;

FIG. 4 is a schematic side view of a test configuration utilized incharacterizing a benefit of an embodiment of the present invention, and;

FIG. 5 is a perspective partial view of a crankshaft torsional vibrationdamper as described above for FIG. 2 in combination with a drive belt aspart of an accessory drive assembly.

DETAILED DESCRIPTION

Referring to FIG. 1, a crankshaft torsional vibration damper 10constructed in accordance with an embodiment of the present invention isshown generally. The damper 10 comprises an annular metal hub 12 asshown, coaxially disposed within an inertia member, depicted in FIG. 1as a metal pulley 14. An annular rubber member 16 comprising an outersurface 28 and an inner surface 34, an outside diameter 60, a thickness62 and an axial width 64, is disposed, optionally under compression inthe range of up to about 50% between the hub 12 and pulley 14, andprovides damping and/or vibration isolation characteristics to theassembly as is well known in the art. In the present context, the terms“inner” and “outer” are not used to describe specific, absolutelocations, but rather are used to convey the general spatialrelationship between the described parts.

The hub 12 comprises an outer surface 26 in adhering contact with therubber member's inner surface 34, and furthermore includes a centraltransverse elongate tube 18 for receiving a mounting axle (not shown,but conventional) and having an aperture 30 for receiving a mountingbolt or support (not shown, but conventional) within an automotiveaccessory drive system. In the embodiment shown, integral connectingmembers or arms 32 extend generally from the tube 18 toward the outerperiphery 33 of the hub 12, to connect the tube 18 to the balance of thehub body. Alternatively, but less preferably due to the added expenseand weight of such configuration, the hub 12 could comprise anessentially solid disc containing a central aperture for supporting thehub within the drive assembly, or any other suitable configurationwhereby the hub's mounting point, illustrated in FIG. 1 as the elongatetube 18, is sufficiently engaged with or connected to its rubber membercontact point 26.

In the embodiment shown, the pulley 14 includes an inner surface 20 inadhering contact with the outer surface 28 of the rubber member 16, andan opposite, drive-member engaging surface 22 characterized in theillustrated embodiment by an alternating arrangement of projections 21and depressions 23 forming grooves as shown for receiving and providingdriving engagement with a suitably-configured drive member, e.g., amulti-v-ribbed belt 35 as shown in FIG. 5, as part of an automotiveaccessory drive assembly.

As the hub 12 and pulley 14, any suitable and/or conventional materialmay be employed, including plastics, rubbers and metals, such as steelincluding galvanized, phosphated and stainless varieties, cast iron,brass, zinc or aluminum, but which is preferably a metal such as iron orsteel, and may moreover contain alloy metals, e.g., chromium and nickel,tungsten, molybdenum, manganese, vanadium, chromium, cobalt andzirconium, in conventional amounts, e.g. of from 0 to about 25%. Thesecomponents may be formed by any conventional and/or suitable method,such as by machining, spinning or by otherwise forming suitableconfigurations. In an embodiment associated with the description setforth below for FIG. 1, both the hub 12 and the pulley 14 are formed ofspun steel. For other applications one may prefer that the pulley 14 beformed of machined cast iron.

As the rubber member, any suitable and/or conventional cured elastomercomposition may be employed, which may be selected by the skilledpractitioner to exhibit suitable strength, flexibility, flex fatigueresistance, compression set, damping and/or isolation characteristics,etc., for a given application. The materials for utilization as therubber member 16 in accordance with exemplary embodiments of the presentinvention are described in further detail below.

Referring to FIG. 2, a second type of crankshaft torsional vibrationdamper 40 is shown. The damper 40 includes a hub 12, a pulley 14 and arubber member 16 as set forth above in the description provided for FIG.1, but in this embodiment, the pulley drive member-engaging surface 22possesses an alternative configuration characterized by a separation ofsuch surface 22 from that surface of the pulley in contact with therubber member 16, with connection of the surface 22 to the balance ofthe pulley 14 by a transverse connecting member 19 perpendicular to thedrive member engaging surface 22.

Referring to FIG. 3, a third type of crankshaft torsional vibrationdamper 50 is shown generally. The damper 50 includes a hub 12, a pulley14 and a rubber member 16 as set forth above in the description providedfor FIG. 1. In this embodiment however, the pulley's drivemember-engaging surface 22 possesses yet another alternativeconfiguration characterized by a first belt-engaging surface 52 having agrooved profile as described above for FIG. 1, and an integral secondbelt engaging surface 54, set at a radius less than that of the firstbelt-engaging surface 52 as shown, and possessing a V-shapedcross-sectional profile formed by a pair of outwardly extending surfaces56, 58, for driving engagement with the driving surfaces of a V-belt ofsuitable dimensions. The skilled practitioner would readily recognizethat the relevant pulley surface could equally well exhibit two groovedbelt engagement surfaces for engagement with two multi-v-ribbed belts;two V-shaped belt engagement surfaces for engagement with two V-belts,or any other combination or configuration appropriate for the particulardrive contemplated. In each case, the invention described herein, whichis related to the fixation of the rubber member 16 between the hub 12and the pulley 14 at the pulley surface remote from the drivemember-engaging surface(s), would provide substantially the samebenefits. The alternative configurations set forth herein are merelyillustrative of several damper configurations which may be appropriatefor one particular drive or another, and are not meant to limit thescope of the present invention as set forth in the appended claims.

In addition, while each of the crankshaft torsional vibration dampersillustrated in the several figures include flat rubber-to-metalinterfaces, as indicated in FIG. 1 for example in the relationshipbetween pulley inner surface 20 and rubber member outer surface 28, itwill be readily recognized that any suitable alternative configurationmay be employed as appropriate for a given application. For example, therubber member itself and one or both of the relevant hub and pulleysurfaces to which the rubber member is chemically bonded according tothe present invention may include one or more curvatures or projections.This technique could be used for example to reduce crankshaft bendingvibration, or to contribute a mechanical component to the chemical bondproduced through the practice of the present vibration. An example ofcurvatures of the type that may contribute one or more suchcharacteristics is set forth in U.S. Pat. No. 5,231,893.

Moreover, while the exemplary figures set forth herein illustratevarious crankshaft torsional vibration dampers, the subject invention isnot intended to be limited to such parts, but is instead applicable toany bonded part wherein a rubber member is bonded to at least a secondsubstrate, such as rubber-to-metal bonded part, including for examplerubber-viscous vibration isolation dampers and other types of torsionalvibration dampers including dual-mode torsional vibration dampers,camshaft torsional vibration dampers, driveshaft torsional vibrationdampers; shaft dampers, shock cells, vibration isolators, vibrationisolation mounts, vibration dampers, couplings, suspension bushings,transmission- and axle seals, tires, belts, hose and rolls. Examples ofsuch articles are described in U.S. Pat. No. 4,477,302 to Leblanc etal., U.S. Pat. No. 5,231,893 to Sisco et al., U.S. Pat. No. 4,368,807 toMcLean, U.S. Pat. Nos. 4,223,565, 5,660,256, and 5,575,869 to Fujiwaraet al. Non-limiting examples of belt constructions and processestherefore are disclosed in U.S. Pat. Nos. 2,507,852, 3,078,206,3,138,962, 3,250,653, 3,772,929, 4,066,732, 4,330,287 and 4,332,576.Non-limiting examples of hose constructions and processes therefore aredescribed in U.S. Pat. Nos. 3,994,761 and 4,000,759 to Higbee. In eachinstance, it is anticipated that the subject invention would provide avery high degree of chemical bonding of the rubber component to theassociated metal or other second surface, optionally in the absence of aseparate rubber-to-metal adhesive applied at the rubber-to-metalinterface. Moreover, while the description provided above in relation tothe figures is directed to rubber-to-metal bonded parts, the subjectinvention may likewise be used in the construction of bonded partswherein the second substrate to which the rubber member is bonded isformed of a material other than metal. Such materials may include forexample, plastic; rubber, including uncured, cured or partially curedrubber; or thermoplastic elastomer.

Turning now to a description of the materials for utilization in formingthe rubber member 16 in the practice of an embodiment of the presentinvention, any suitable elastomer composition may be employed, whichcomprises at least one elastomer, at least one curative, and at leastone adhesive adjuvant or coagent such as a rubber-to-metal adhesiveadjuvant or coagent. Within the present context, the terms, “elastomer”and “rubber” will be utilized interchangeably to denote any natural orsynthetic high polymer having the properties of deformation and elasticrecovery upon curing or vulcanization; and the terms “curative”, “curingagent”, “cross-linking agent” or “vulcanization agent” will be utilizedinterchangeably to denote a substance that is capable of converting anelastomer from thermoplastic to thermosetting, i.e., that is capable ofcross-linking the elastomer molecules. In the present context, theterms, “rubber-to-metal adhesive adjuvant” (or “adjuvant”) and“rubber-to-metal adhesive coagent” (or “coagent”) are usedinterchangeably to denote a material that provides, promotes orcontributes to adhesion between itself and one or more other materials,or between two or more such materials, through mechanical- and/orchemical bonding, the latter of which may include any type, includingbut not limited to covalent bonding, ionic bonding, dipole interactionssuch as hydrogen bonding, etc.

Suitable elastomers that may be utilized for this purpose include forexample ethylene-alpha-olefin elastomers (such as ethylene propylenecopolymers (EPM), ethylene propylene diene terpolymers (EPDM), ethyleneoctene copolymers (EOM), ethylene butene copolymers (EBM), ethyleneoctene terpolymers (EODM); and ethylene butene terpolymers (EBDM));ethylene/acrylic elastomer (EAM), polychloroprene rubber (CR),acrylonitrile butadiene rubber (NBR), hydrogenated NBR (HNBR),styrene-butadiene rubber (SBR), alkylated chlorosulfonated polyethylene(ACSM), epichlorohydrin (ECO), polybutadiene rubber (BR), natural rubber(including synthetic polyisoprene) (NR), chlorinated polyethylene (CPE),brominated polymethylstyrene-butene copolymers,styrene-butadiene-styrene- (S-B-S) andstyrene-ethylene-butadiene-styrene (S-E-B-S) block copolymers, acrylicrubber (ACM), ethylene vinyl acetate elastomer (EVM), and siliconerubber, or a combination of any two or more of the foregoing. In anembodiment of the present invention the elastomer is anethylene-alpha-olefin elastomer such as EPDM.

Within the present context, the terms “bonded” and “adhered” unlessspecifically noted otherwise, are used interchangeably as wellrecognized in the art, to denote a strong or substantial fixationbrought about by chemical reaction. This condition is characterized byany increased force required to separate the relevant substratescompared to that force required to separate the substrates in theabsence of such condition. Bonding strength may exceed rubber tearstrength in the practice of the present invention, resulting in cohesivefailure of the rubber, but cohesive failure is not necessary toestablish that some bonding is achieved within the context of thepresent invention.

In the practice of an embodiment of the present invention, it has beenfound that elastomer composition properties such as elastomercrystallinity, damping capability and viscosity or modulus havevirtually no appreciable impact on the level of adhesion achievedbetween the relevant rubber and metal surfaces. The skilled practitionerwill recognize however that one or more such properties may becontrolled or selected to influence the overall performance orcapability of, e.g., a crankshaft torsional vibration damper constructedin accordance with an embodiment of the present invention, as desiredfor a given application. Thus, while not necessary in the practice ofthe present invention, ethylene-alpha-olefin elastomers having anethylene content in the range of from about 40 to about 80% by weight;more preferably of from about 50 to about 75% by weight; and mostpreferably of from about 50 to about 62% by weight have favorably beenemployed as the base elastomer in accordance with an embodiment of thepresent invention. A Mooney viscosity of such elastomer, of from about10 to about 100 at 125° C., more preferably of from about 20 to about 75at 125° C. and most preferably of from about 50 to about 75 at 125° C.has moreover been found to achieve good results in accordance with anembodiment of the present invention.

EPDM materials that may for example be used in the practice ofembodiments of the present invention include those available under thereferences KELTAN by DSM Chemical Co.; silicone-modified EPDM orEPDM/silicone rubber blends including those available under thereference ROYALTHERM by Uniroyal Chemical Co., and those EPDM materialsavailable under the references VISTALON by Exxon, NORDEL by DuPont-DowElastomers, and ROYALENE by Uniroyal Chemical Co.

In accordance with the present invention, the composition furthermorepreferably includes at least one adhesive adjuvant, and in an embodimentof the present invention, includes at least one rubber-to-metal adhesiveadjuvant, for providing improved adhesion of the rubber member to themetal components upon vulcanization thereof in accordance with anembodiment of the present invention described in further detail below.Suitable adjuvants include those materials generally classified as TypeI coagent compounds, exemplified by polar, relatively low molecularweight materials such as acrylates, methacrylates and certainbismaleimides; and those materials generally classified as Type IIcoagent compounds, exemplified by the low polarity, network-buildingmaleated polybutadienes. Further examples, characteristics and suitableusage amounts of Type I and Type II coagents are described in the paper,“1,2 Polybutadiene Coagents for Improved Elastomer Properties” by R. E.Drake et al., Ricon Resins, Inc., as presented at the American ChemicalSociety Rubber Division Meeting in November 1992. Type I and Type IIcoagents are furthermore disclosed in U.S. Pat. No. 5,300,569 to Drakeet al., and as polyfunctional monomers in U.S. Pat. No. 4,857,571, thedisclosures of which with respect to exemplary coagents and theirrelative useful amounts in elastomer compositions are herebyspecifically incorporated by reference.

In combination with the ethylene-alpha-olefin elastomers utilized inexemplary embodiments of the present invention, such Type II adjuvantsinclude for example maleated polybutadienes, such as maleinized1,2-polybutadiene resins (70-90%) exemplified by the material availableunder the trademark RICOBOND 1756 by Ricon Resins; and the Type I metalsalts of alpha-beta unsaturated organic acids set forth for example inU.S. Pat. No. 5,610,271 to Yarnell et al., the contents of which withregard to such salts and their beneficial use in such elastomer systemsis herein specifically incorporated by reference. Such salts includezinc diacrylate and zinc dimethacrylate including those available underthe trademarks SARET 633, SARET 634 and SARET 708 by The Sartomer Co. Inparticular, zinc dimethacrylate may beneficially be utilized in amountsof from about 1 to about 50 parts per hundred weight of elastomer(“phr”), more preferably of from about 10 to about 40 phr, and mostpreferably of from about 15 to about 30 phr. Maleated polybutadieneresins when used may be favorably incorporated in the elastomercompositions in the same to slightly lower amounts, e.g., of from about1 to 50 phr; more preferably of from about 5 to 40 phr; and mostpreferably of from about 10 to 30 phr. Additionally, imide coagents suchas that exemplified by N,N′-m-phenylenedimaleimide available under thetrademark HVA-2 by DuPont Chemical Co. may be used singly in about thesame foregoing amounts, or may optionally but favorably be used incombination with one or more of the above-described adjuvants/coagents,in amounts of from about 0.25 to about 5 phr; more preferably of fromabout 0.50 to about 2.5 phr; and most preferably of from about 0.75 toabout 1.50 phr.

It is believed that those materials conventionally classified astackifiers may moreover be utilized singly or in combinations of two ormore thereof as adhesive adjuvants, and have furthermore been used incombination with one or more of the foregoing Type I and/or Type IIcoagents in the practice of the present invention. Such materials mayinclude for example terpene resins, terpene-phenol resins, rosins,aromatic hydrocarbon tackifiers, polyterpene resins, hydrocarbon resins,and preferably those available under the references WINGTACK fromGoodyear and RESINEX from Harwick. These materials when employed in thepractice of the present invention may be utilized in amounts of fromabout 1 to about 100 phr, more preferably from about 10 to about 75 phr,and most preferably of from about 20 to about 60 phr.

For utilization in an embodiment of the present invention, the elastomercomposition optionally but preferably includes one or more additionalconventional rubber composition additives, e.g., fillers, oils,vulcanization agents, activators and accelerators; scorch retarders,tackifiers, processing aids etc., in amounts conventionally employed, toform elastomeric materials useful in the practice of the presentinvention. For example, suitable fillers may be reinforcing,non-reinforcing, semi-reinforcing types or combinations of theforegoing, and may include carbon blacks; silica; clay; talc, etc. Inparticular, such fillers may be employed in the practice of the presentinvention in amounts of from about 0 to about 200 phr; more preferablyof from about 10 to about 150 phr, and most preferably of from about 25to 100 phr. In those applications wherein static conductivity isdesirable, such as in the construction of various vibration dampers, theincorporation of a suitable conductive black may be particularly useful.

The elastomer compositions according to an embodiment of the presentinvention may be cured using any suitable and/or conventional curativeor vulcanization system suitable for use with the base elastomer,including those employing sulfur, organic peroxide or other free-radicalinducing material, and combinations of two or more thereof, incure-effective amounts. In an embodiment the elastomer composition iscured in at least two stages, through a cure-effective amount of acurative selected from organic peroxides, organic peroxides blended withfrom about 0.01 to about 1.0 phr of sulfur, ionizing radiation, andcombinations of two or more of the foregoing. For utilization with theethylene-alpha-olefin elastomers of an embodiment of the invention,peroxide curatives are preferred, being present in the elastomercomposition at levels of from about 0.5 to 25 phr; more preferably offrom 1 to 20 phr; and most preferably of from about 2 to about 15 phr.

In an embodiment of the present invention, at least two separatecuratives or cure systems (i.e., wherein the cure system may include asingle curative or blends or mixtures of two or more individualcuratives), are employed to cure the elastomer composition. Suchcuratives may moreover be advantageously selected such that each suchcurative or cure system possesses an activation temperature rangedistinct from the other. In a further embodiment, two such curatives areemployed in the elastomer compositions of the present invention,activation of each of which being triggered by exposure to a set ofconditions, including temperature, pressure and exposure period,different from the other. For substantially equal exposure periods andpressures, activation temperatures of such two curatives according to anembodiment at least five (5) degrees Centigrade apart from one another;more preferably at least fifteen (15) degrees Centigrade apart from oneanother; and most preferably at least twenty five (25) degreesCentigrade apart from one another may be beneficially employed. Thisaspect of this embodiment of the present invention is further describedin the Illustrations below. Exemplary materials exhibiting respectiveactivation temperatures beneficial in the practice of the presentinvention include as the first curative,1,1-Di-(t-butylperoxy)-3,3,5-trimethylcyclohexane such as that availableunder the trademark VAROX 231XL by R.T. Vanderbilt; and as the secondcurative, 2,5-dimethyl-2,5-Di-(t-butylperoxy) 3-hexyne such as thatavailable under the trademark VAROX 130XL by R.T. Vanderbilt.

According to an embodiment of the present invention, this first curativemay favorably be incorporated in the elastomer compositions according tothis embodiment, in amounts of from about 0.2 to about 20 phr; morepreferably of from about 0.3 to about 15 phr, and most preferably offrom about 0.4 to about 10 phr. According to this same embodiment, thissecond curative may be incorporated in the elastomer compositions inamounts of from about 0.05 phr to about 25 phr; more preferably of fromabout 0.1 to about 20 phr; and most preferably of from about 0.2 toabout 15 phr. Suitable ratios of first to second curatives within theelastomer compositions according to this embodiment of the invention maybe from about 1:20 to about 30:1; more preferably of from about 1:12 toabout 20:1; and are most preferably from about 1:7 to about 10:1.

Elastomer composition properties such as post-first-step cure modulus,adhesion level and tear strength have been found to vary with both theratio of the first curative to the second curative, as well as the totalamount of each curative present in the elastomer composition. Thoseskilled in the relevant art would readily appreciate the variouspermutations that can be achieved, with both positive and negativeimpact on the resultant properties of the cured elastomer composition,through varying these individual curative ratios and amounts asindicated in the illustrations set forth below, and would be able totailor the specific ratios and amounts of curatives within the scope ofthe present invention as appropriate for a given application.

As indicated above, further conventional rubber additives may beemployed in forming the elastomer compositions useful in the practice ofthe present invention, e.g., process aids such as zinc stearate may beutilized as desired in conventional amounts, e.g., up to about 5 phr.Plasticizers and/or extender oils or other processing aids mayoptionally be utilized in any suitable amount, e.g., up to about 300 phrand more preferably of from about 20 to about 100 phr; vulcanizationaccelerators and/or retarders may optionally be employed in any suitableamount, e.g. up to about 10 phr; and antioxidant systems may optionallybe employed in any suitable amount, e.g. up to about 5 phr mayoptionally be utilized.

In an embodiment of the invention wherein the elastomer utilized in theelastomer composition is an ethylene-alpha-olefin elastomer, e.g., EPDM,having a relatively high molecular weight and/or narrow molecular weightdistribution, the elastomer composition optionally further comprises asuitable paraffinic or naphthenic oil as a processing aid, withparaffinic oils being more preferred for utilization with suchelastomers. Such oils may optionally be utilized in amounts up to about300 phr; or from about 10 to about 250 phr; or at from about 50 to about150 phr, to decrease compound viscosity as needed to achieve propermixing of composition constituents or to adjust the compound hardness orto simply reduce the compound cost. Suitable paraffinic oils include forexample those available under the references SUNPAR by Sun Refining Co.;and SHELLFLEX by Shell Chemical Co. Moreover, paraffinic oil or someportion thereof may be provided through addition of the particularelastomer employed. For example, the EPDM elastomer available under thetrademark KELTAN K7441A by DSM is believed to include 75 phr ofparaffinic oil per 100 phr of polymer (and for this reason, is includedin formulations set forth in Tables 1 and 2 below, at 175 phr, i.e., 100phr constituting the elastomer portion and the remainder constitutingthe oil).

According to one embodiment thereof, the present invention provides aprocess for bonding rubber to metal which avoids the drawbacks of priorart processes, and includes the steps of placing an uncured elastomercomposition comprising at least a base elastomer, at least onerubber-to-metal adhesive adjuvant and at least one curative as describedabove into a shape-forming mold, of the type utilized in any suitableand/or conventional press molding process, e.g., injection molding,transfer molding and compression molding; and applying sufficienttemperature over a sufficient period of time at a sufficient pressure tosubstantially, but not fully cure the elastomeric material; placing theso formed rubber member in contact with at least one metal substratesurface and applying sufficient temperature over a sufficient period oftime to substantially fully cure the rubber member. Through thisprocess, sufficient adhesion is achieved between the rubber member soformed and the metal substrate in the absence of rubber-to-metaladhesives applied directly at the rubber-metal interface such that onemay avoid utilization of such potentially harmful and/or costly metaladhesives in such process, without relying entirely on any compressionand frictional forces that may be present to hold the rubber member inplace. It has been surprisingly found that by following the steps ofthis process in accordance with the description set forth herein, robuststrength of adhesion is achieved, sufficient to allow for utilization ofthis process in high vibration and/or shock applications exemplified byautomotive crankshaft torsional vibration dampers as illustrated in thefigures described above. This phenomenon is described more fully belowin the accompanying Illustrations.

In an embodiment of the present invention particularly useful in themanufacture of metal-rubber composite structures exemplified bytorsional vibration dampers, wherein the rubber member is disposed,optionally under compression, between two or more outer metal surfaces,the process preferably includes the steps of curing the elastomercomposition in at least two steps, wherein in the first curing step,preferably performed with the uncured elastomer in a shape-forming mold,the elastomer is less than fully cured; and in the second curing step,preferably performed with the less-than-fully cured elastomercomposition in contact with the relevant metal surface, the elastomer isat least substantially fully cured. The level of adhesion obtained inbonding rubber to metal using the two step curing process of anembodiment of the present invention has been found to generally be at alevel of from about 10% to about 100% of that level of adhesion achievedthrough one-step vulcanization bonding for identical or substantiallycomparable compositions, depending primarily on the level of metaladhesive coagent used.

Two stage curing in accordance with an embodiment of the subjectinvention however, has been found to provide improved durability of theassociated rubber member compared to comparable parts assembledutilizing vulcanization bonding techniques. The skilled practitionerwould readily recognize that in vulcanization bonding uncured elastomercompositions directly to metal, at least some rubber shrinkage occursalmost immediately upon allowing the material's temperature to fallbelow its characteristically high vulcanization temperature. In theassembly of rubber-to-metal bonded parts exemplified by crankshafttorsional vibration dampers wherein the rubber member is disposedbetween two outer metal surfaces, as the vulcanized assembly is broughtto room temperature following vulcanization, the so-affected rubbermember exhibits some level of shrinkage and thus is stretched betweenthe metal surfaces to which it is bonded. This results in the rubberresiding under tension between the metal surfaces. This tension leads tocrack propagation and associated defects and ultimately to prematurefailure. The flexing to which the damper or comparable assembly wouldlikely be exposed in operation would furthermore generally exacerbatethis problem.

The two-stage vulcanization process of an embodiment of the presentinvention avoids such difficulties. In particular, by exposing theelastomeric composition to an initial partial curing operation prior toits application to at least one of the associated metal surfaces, anyshrinkage that may occur during vulcanization at this stage can beaccommodated through an appropriate modification or selection of molddimensions. Subsequently, when the partially cured molded elastomercomposition is disposed under compression between both of the associatedmetal surfaces, an additional curing operation can be performed,sufficient to fully cure the elastomer and to bond it to the metalwithout causing the elastomer to go into a state of tension.

One of ordinary skill in the relevant art would readily appreciate thatin addition to the specific examples set forth herein, a number ofprocess steps or configurations would lend themselves equally well tothe method of the present invention in various embodiments thereof. Thusfor example, for those bonded parts comprising a rubber member bonded toat least two outer members, the first, partial curing step could beperformed with the uncured elastomer composition in contact with asurface of at least a first such outer member such that the rubbermember is vulcanization bonded to such outer member surface, and thesecond curing step could be performed with the partially cured elastomercomposition in contact with a surface of a second such outer member.Such variations are contemplated within the scope of the presentinvention, which is limited only by the appended claims.

As indicated above, one advantage of conventional post-vulcanizationbonding techniques is that since the rubber member is fully cured priorto its placement between the outer metal surfaces, it does not exhibitsignificant shrinkage. Variables such as the compression set of theelastomer, and the level of compression applied to the rubber betweenthe metal may be controlled in such a manner to achieve a compositionthat is in a neutral state at a given temperature, above which itgenerally resides under compression. In the practice of the presentinvention, it has surprisingly been found that by partially curing theelastomeric composition in a molding operation as described herein to astate of cure of at least about 20%, preferably of from about 30% toabout 99%, and preferably of from about 50% to about 95%, as determinedin accordance with ASTM D5289 and utilizing Monsanto moving dieRheometer techniques and apparatus, a second curing operation cansubsequently be performed, preferably with the elastomeric compositionin contact with the relevant metal surface(s), and under an appliedforce sufficient to achieve rubber compression of from about 1% to 60%,or from about 5% to about 50%, or from about 10% to about 40%, to fullycure the composition, to provide robust strength of adhesion of thefully vulcanized rubber member in the absence of additional adhesivecompositions at the rubber-to-metal interface, and to maintain therubber member in essentially a neutral, i.e., non-tensioned state at itsintended operating temperature range, of, e.g., −20° C. to about 120° C.At relatively lower states of cure accomplished in the first cure step,relatively higher levels of adhesion may be established, which may bedesirable for those applications wherein rubber compression (orpreventing the rubber from going into tension at its expected operatingtemperature) is not needed.

Illustrations and Examples

In the following Illustrations and Examples:

Keltan 7441A denotes EPDM available under that reference by DSM.

Keltan 55 denotes EPDM available under that reference by DSM.

Keltan 2340A denotes EPDM available under that reference by DSM.

Royaltherm 1411 denotes silica-modified EPDM/silicone blend availableunder that reference by Uniroyal Chemical Co.

Royalene 580 HT denotes EPDM available under that reference by UniroyalChemical.

Exxon Butyl 268 denotes isobutylene-isoprene elastomer available underthat reference from Exxon Chemical Americas (or R. T. Vanderbilt).

Vistanex MM L-140 denotes Polyisobutylene available under that referencefrom Exxon Chemical Americas.

Vamac D denotes ethylene/acrylic elastomer available under thatreference from DuPont Chemical Co.

Hypalon 40 S denotes chlorosulfonated polyethylene available under thatreference from DuPont Chemical Co.

Tyrin CM denotes denoted chlorinated polyethylene available under thatreference from DuPont Dow Chemical Co.

Kraton G1652 denotes S-EB-S block copolymer blends available under thatreference from Shell Chemical.

Kraton D1112P denotes S-B-S block copolymer blends available under thatreference from Shell Chemical.

Kraton D1107 denotes S-B-S block copolymer blends available under thatreference from Shell Chemical.

Trilene 65 DLCA denotes 72% base on silicate powder peroxide or sulfurcure available from Natrochem.

N550 denotes carbon black N550.

N472 denotes conductive carbon black N472 under the reference STERLINGXC-72 by Cabot.

N293 denotes conductive carbon black type N293 under the referenceSTERLING C by Cabot.

HiSil 233 denotes precipitated, hydrated amorphous silica available fromPPG.

Maglite D denotes magnesium oxide available under that reference by CPHall.

Franklin T-14 denotes calcium carbonate from Franklin Industries.

Dixie 2.6 denotes clay from R.T. Vanderbilt.

Mistron Vapor Compac denotes magnesium silicate (talc) available underthat reference from Luzenac America, Inc.

McNamee Clay denotes Kaolin (soft) clay (hydrated aluminum silicate)available under that reference from R.T. Vanderbilt.

HVA-2 denotes N,N′-m-phenylenedimaleimide (imide coagent) availableunder that reference by DuPont Dow Chemical Co.

SARET 633 denotes zinc diacrylate available under that reference bySartomer Co.

SARET 634 denotes zinc dimethacrylate available under that reference bySartomer Co.

RICOBOND 1756HS denotes maleated polybutadiene available under thatreference by Ricon Resins, Inc.

CBS denotes N-cyclohexyl-2-benzothiazylsulfenamideN-t-butyl2-benzothiazol sulfenamide (accelerator) available under that referenceby Harwick.

VAROX 130XL denotes 1,1-Di-(t-butylperoxy)-3,3,5-trimethylcyclohexaneavailable under that reference by R.T. Vanderbilt Co.

VAROX 231 XL denotes 2,5-dimethyl-2,5-Di-(t-butylperoxy) 3-hexyneavailable under that reference by RT Vanderbilt Co.

VULCUP 40 KE denotes 2,2′ bis (tert-butylperoxy diisopropylbenzene) 40%on Burgess KE clay available under that reference by Harwick.

Harmony AW-46 denotes hydraulic oil available under that reference byPetrop-Canada.

Ultima EP-220 denotes a gearbox oil available under that reference byPetro-Canada.

Dascoway 68 denotes a Waylube oil available under that reference by D.A.Stuart, Inc.

Drawsol 165 M denotes draw compound available under that reference byD.A. Stuart, Inc.

S500-US 5% denotes a coolant available under that reference byHangsterfer's Laboratories, Inc. in a 5% concentration in water.

While any conventional or suitable procedure for mixing an elastomercomposition may be employed in the practice of the present invention,for each of the following elastomer compositions numbered E1-E72,processing was carried out as follows. In each case the EPDM or modifiedEPDM polymer or other elastomer or combination of elastomers was firstadded to a 1A Banbury mixer having an inner volume of 16,027 cm³ withmixing at 40 rpm (or, in the case of compositions E4-E26, in a B Banburyhaving an inner volume of 1573 cm³, with mixing at 70 rpm). Afterapproximately one minute, the remaining ingredients with the exceptionof the curatives and, where utilized, accelerators were added, and theresultant mixture was blended until a temperature of 310-315° F.(154-157° C.) was reached or for a maximum time of 8 minutes. Thecuratives were then added on an open two-roll mill at a mixturetemperature less than 100° C., and the mixture was further mixed suchthat 100° C. was not exceeded. For compositions E18 through E22 of Table2, compositions E27 through E30 of Table 3, compositions E46 through E49of Table 7 and all of the compositions of Table 8, the order of additionwas switched (exclusive of curative and accelerator addition) such thatthe elastomer constituent was added approximately one minute after theother powdered ingredients. Unless otherwise noted, the componentamounts listed in the tables and throughout the following Illustrationsfor elastomer compositions, are expressed in terms of parts perhundredweight of elastomer (“phr”). Where shown in the followingexamples, the compositions employed as an optional constituent aparaffinic or naphthenic process oil, e.g., Sunpar 150, -2280 orPlasthall 7050, as a plasticizer and/or mixing aid. Those compositionsrepresented in the following illustrations generally further comprisedone or more process aids (such as to promote mixing and/or millrelease), antioxidants and/or antiozonants of conventional types for thevarious elastomers employed, and in conventional amounts. Thus forexample the compositions employing EPDM as the base elastomer generallyfurther comprised as optional constituents 5 phr of zinc oxide, 1.5 phrof zinc stearate, 0.6 phr of a 99% triethanolamine and 1.5 phr of anantioxidant.

Unless and then to the extent otherwise indicated below, Lap shearadhesion results provided in the following tables were obtained usingsteel tabs 72, 74 each measuring 1 inch by 2.5 inches, and molded rubberslabs 70 measuring {fraction (3/16)} of an inch in thickness by 1 inchsquare, assembled according to the method of ASTM D816 such that therubber sample was substantially fully covered on both relevant surfacesby the metal slab, as represented in the schematic rendering of FIG. 4,under an applied force sufficient to achieve 25% rubber compression. Forthe examples set forth in Tables 1 and 2, the steel slabs were gritblasted and alkali washed utilizing conventional techniques prior to theapplication of the elastomer composition, and a conventional assemblylubricant was applied to the surface of the elastomer compositions afterthe first cure step. For the remainder of the elastomer compositions,the same cleaning procedures were utilized, unless and to the limitedextent otherwise noted, except that the steel slabs were not gritblasted.

Unless and if so, then to the extent otherwise specifically provided,the first step cure employed in injection- or compression molding therubber slabs in the following Illustrations as indicated was generallyperformed for 4 or 5 minutes at 160° C., but in each case to achieve apartially cured elastomer composition capable of retaining the shapeimparted to it in the mold. The second step cure, performed in a hot airoven (i.e., generally at atmospheric pressure) with the partially curedelastomer slabs in contact with and disposed between the steel slabs,was sufficient to provide an actual rubber temperature of 190° C. for atleast 10 minutes, to essentially fully cure the elastomer composition asdetermined utilizing Monsanto moving die Rheometer techniques andapparatus and in accordance with ASTM 5289. The Lap Shear adhesionspecimens were pulled at a rate of 0.5 inches per minute on a standardInstron™ tensile test machine to a point of adhesive or cohesivefailure. The peak load so achieved is in each case reported in theTables in pounds, or equivalently due to the above-described dimensionsof the test specimens, in pounds per square inch.

In general, for the Lap Shear adhesion results reported in the followingtables, adhesive failure, i.e., failure at the rubber-to-metalinterface, was generally the mode of failure for all reported results upto approximately 200 lbs/in² (1.38 MPa), while for generally allreported values greater than about 200 lbs/in² (1.38 MPa), at least somelevel of cohesive failure, i.e., rubber tearing, occurred.

Illustration A

Exemplary effects of varying rubber-to-metal adhesive adjuvant type andlevel, and curative type and level, are shown in Tables 1-3. Asexpected, the degree of adhesion obtained is shown to generally increasewith increasing amount of rubber-to-metal adhesive adjuvant in thecompositions. Several examples employed a combination of two Type Icoagents, namely Saret 634 plus HVA-2. E9 and E10 illustrate the use ofa Type II metal adhesive coagent, i.e., Ricobond 1756HS.

The use of a single peroxide and two stage curing in accordance with anembodiment of the present invention is illustrated in Compositions E1and E2 and E3. The use of mixed peroxide and sulfur cures in two stagecuring according to an embodiment of the present invention isillustrated in Compositions E21 and E22. The remaining examples inTables 1-3 illustrate the wide range of peroxide levels useful for twostage curing in accordance with embodiments of the present invention.TABLE 1 Compound Ingredients E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 Royaltherm1411 100 100 0 0 0 0 0 0 0 0 Royalene 580HT 0 0 100 0 0 0 0 0 0 0 Keltan7441A 0 0 0 175 175 175 175 175 175 175 N472 0 0 40 47 47 47 47 47 47 47N550 3 5 0 57 57 57 57 57 57 57 HiSil 233 6 10 0 0 0 0 0 0 0 0 Sunpar2280 0 0 60 60 60 60 60 60 60 60 Calight RPO 0 0 10 0 0 0 0 0 0 0 HVA-20 0 1 0 0 0 0 0 0 0 Saret 634 3 5 20 5 5 15 15 15 0 0 Ricobond 1756HS 00 0 0 0 0 0 0 15 15 Vulcup 40KE 3 3 3 0 0 0 0 0 0 0 Varox 231XL 0 0 01.88 0.94 1.88 3.75 0.94 3.75 0.94 Varox 130XL 0 0 0 3.22 3.75 3.22 2.153.75 2.15 3.75 Peak Load (lbs./in²) 83 62 141 37 44 103 92 44 74 71

TABLE 2 Compound Ingredients E11 E12 E13 E14 E15 E16 E17 E18 E19 E20 E21E22 Keltan 55 100 100 100 100 100 100 100 0 0 0 100 100 Royalene 580HT 00 0 0 0 0 0 100 100 100 0 0 N472 65 65 65 65 65 65 65 40 40 40 65 65Sunpar 2280 20 20 20 20 20 20 20 10 10 10 20 20 Saret 634 20 20 20 20 2020 20 20 20 20 20 20 HVA-2 1 1 1 1 1 1 1 0 0 0 1 1 Varox 231XL 7.5 3.81.9 11.3 5.6 2.8 1.7 3.4 5.4 7 2.8 2.8 Varox 130XL 4.3 6.4 7.5 6.4 9.711.3 12.0 0.6 1 0.4 11.3 11.3 Sulfur 0 0 0 0 0 0 0 0 0 0 0.2 0.3 CBS 0 00 0 0 0 0 0 0 0 0 0.6 Peak Load 134 345 435 180 210 177 206 167 197 191174 162 (lbs/in²)

TABLE 3 Compound Ingredients E23 E24 E25 E26 E27 E28 E29 E30 Keltan7441A 175 175 175 175 175 175 175 175 N472 88 88 90 40 45 45 40 90 N5500 0 0 80 30 30 80 0 Sunpar 2280 20 20 50 60 30 30 60 15 Saret 634 30 3030 30 30 30 30 30 HVA-2 1 1 1 0.5 1 0 1.5 1 Varox 231XL 2.8 1.8 1.8 0.91.8 1.8 5 5 Varox 130XL 11.3 7.5 7.5 9.5 7.5 7.5 3.2 0.6 Peak Load 320741 665 473 387 298 307 142 (lbs./in²)Illustration B

Exemplary effects of varying the levels of each of two peroxidecoagents, two carbon black types and paraffinic oil of respectiveelastomer compositions according to embodiments of the subject inventionare illustrated in Table 4. In each case, uncured elastomer compositionswere prepared utilizing the respective constituents set forth in theTable 4, as described above, and elastomer slabs as described above forLap Shear adhesion analysis were formed therefrom, by compressionmolding individual specimens under first stage curing conditions of 4minutes at 160° C. For each composition noted below, thus-preparedpartially cured elastomer slabs were then applied under 25% compressionbetween two steel test slabs, each having the dimensions noted above forLap Shear adhesion analysis metal slabs. For the peak load results inTable 4 marked “WITH P80 LUBE”, a thin coating of P80 lubricating oilavailable from International Products Corp. was applied to the relevantmetal surfaces prior to application of the partially cured elastomerslabs. These assemblies to which lubricating oil were applied were eachallowed to sit for 4 hours. Second stage curing for all examples wasthen conducted in a hot air oven to a temperature of 204° C. for 40minutes. Lap Shear adhesion analysis in accordance with ASTM D816 wasthen performed both at room temperature (roughly 20° C.) and at 100° C.,with a pull rate of 0.5 inches per minute, and both the peak loadachieved and the percent rubber coverage upon failure were recorded.Percent rubber coverage indicates the level of cohesive versus adhesivefailure that occurred for the test specimens, with zero percent rubbercoverage on the steel surface indicating adhesive failure.

The adhesion results set forth in Table 4 indicate that excellentadhesion of cured elastomer slabs to steel in accordance with thepresent invention can be achieved utilizing a variety of conventionalelastomer composition constituents at various amounts. While asindicated above the level of adhesive adjuvant in the elastomercomposition has the greatest impact on the composition's level ofadhesion to metal in accordance with the subject invention, it isnotable that by varying, e.g., reinforcement types and/or levels, orperoxide level, one can dramatically impact the resultant strength ofadhesion. This is apparent for example in the results provided forCompositions E33, E35 and E37, each of which contains 30 phr of zincdimethacrylate adhesive adjuvant. TABLE 4 E31 E32 E33 E34 E35 E36 E37E38 E39 E40 Compound Ingredients Keltan 7441A 175 175 175 175 175 175175 175 175 175 N472 40 50 40 40 40 40 40 50 50 40 N550 40 20 30 50 8080 0 40 50 0 SUNPAR 2280 60 60 60 60 60 60 20 60 40 20 SARET SR-634 2030 30 10 30 30 30 10 30 30 HVA-2 1.5 0.5 1 0.5 1.5 0.5 1.5 1.5 1.5 0.5VAROX 130XL 5.5 5.5 9.5 9.5 5.5 9.5 5.5 5.5 5.5 9.5 VAROX 231XL 1.8 2.71.8 2.7 0.9 0.9 2.7 0.9 2.7 0.9 Adhesion results Peak Load (lbs/in²),20° C., on 339 394 181 98 665 635 130 489 213 126 Steel % rubbercoverage, 20° C., on 5 10 5 0 5 20 1 5 0 0 Steel Peak Load (lbs/in²),100° C., on 108 105 103 23 508 435 62 174 93 65 Steel % rubber coverage,100° C., on 5 10 10 0 95 50 5 10 1 5 Steel Peak load (lbs/in²), 20° C.,on 231 70 12 0 424 473 181 88 339 247 Steel WITH P80 LUBE % rubbercoverage, 20° C., on 5 1 0 0 90 90 35 0 13 5 Steel WITH P80 LUBEIllustration C

The effects of varying the state of cure achieved in a first cure stepare shown in Table 5. In each case, the elastomer slabs were formed byinjection molding with a cure of 2 minutes at 165° C. This first curestep was then extended as shown in Table 5 for the individual examples,to achieve the indicated level of cure, as determined utilizing Monsantomoving die Rheometer techniques and apparatus, according to ASTM D5289.Each of the partially cured elastomer slabs were then assembled for LapShear adhesion analysis as described above applying compression of 25%or 40% as indicated and utilizing the second stage cure conditions setforth in Table 5 below, cycled between −20° C. and 120° C. several timesto simulate thermal stresses a damper would experience in operation, andthen pulled to determine Lap Shear adhesion level as manifested in peakload, at a rate of 0.5 inches per minute on an Instron™ tester. Thesecond step cure times and temperatures in each instance reported inTable 5 were selected to achieve in each instance a substantially fullycured composition in accordance with the procedure set forth above.

As indicated, all of the examples displayed excellent adhesion results,and moreover exhibited some level of cohesive failure, indicating thatthe strength of the chemical bond achieved in the practice of thepresent invention exceeded the tear strength of the rubber in theseinstances. The results indicate a maximum adhesion level atapproximately 70-80% cure in the first stage, but even at 95% cureduring this first stage, excellent results were obtained. Thus, thepresent invention permits one to partially cure the elastomercompositions in a first step performed in a shape forming mold, e.g., aninjection mold, a transfer mold or a compression mold, to a point atwhich the material can easily be removed from the mold and can behandled and manipulated without adversely impacting the shape orintegrity of the so-molded part. Thereafter, the partially curedelastomer composition molded part in an embodiment of the presentinvention can be inserted between or applied to the relevant metalsurface(s), and then cured completely in a second step, whichfurthermore serves to chemically bond the elastomer composition to themetal surface(s) in the absence of any additional adhesive applied atthe relevant rubber-to-metal interface. Thus, the step of applying arubber-to-metal adhesive at the rubber-to-metal interface can beavoided, and production efficiency and flexibility can be greatlyimproved. In addition, in those constructions wherein the rubbermember's tendency to go into a state of tension between outer metalsurfaces is undesirable, e.g., in crankshaft torsional vibration dampersas described above in relation to the accompanying drawings, the presentinvention in an embodiment thereof makes it possible to retain at leastsome level of rubber compression or neutrality within the intendedoperating temperature range. TABLE 5 Composition E24 E24 E24 E25 Secondstep cure Temperature 200° C. 180° C. 160° C. 160° C. Second step CureTime 19 min. 36 min. 155 min. 155 min. Applied Compression 25% 25% 40%40% Peak Peak Peak Peak Load Load Load Load (lbs/in²) (lbs/in²)(lbs/in²) (lbs/in²) First step cure to 50% 431 600 703 603 completionFirst step cure to 60% 778 514 696 648 completion First step cure to 70%481 504 739 642 completion First step cure to 80% 597 860 746 580completion First step cure to 90% 547 562 733 462 completion First stepcure to 95% 549 517 700 442 completionIllustration D

To illustrate the effectiveness of the method of an embodiment of thepresent invention over a broad cure temperature range, the effect onrubber-to-metal adhesion level of varying the second stage cure stepconditions in order in each case to achieve a substantially curedelastomer composition is illustrated in Table 6. In each case, theelastomer compositions were mixed in accordance with the descriptionprovided above, and uncured elastomer specimens were then injectionmolded with a first stage cure of 2 minutes at 165° C. to form partiallycured elastomer slab specimens. These partially cured specimens werethen assembled into Lap Shear analysis specimens as described above,under 25% compression, and utilizing P80 assembly lubricating oilavailable from International Products Corp. applied in a thin layer tothe steel slab surfaces. In each case, the lap shear specimens wereallowed to sit for 4 hours in contact with the lubricating oil-coatedslabs, and then cured as indicated in Table 6, and subsequently pulledaccording to the Lap Shear adhesion analysis procedure set forth above,at a rate of 0.5 inches per minute to a point of failure. In general,the failure mode in all instances shown in Table 6 was cohesive failure.Notably, in the last two examples of Table 6, a total of three curingstages were employed as shown. In general, the results so obtainedindicate excellent adhesion values, but the best results were achievedwith the lowest second stage cure temperatures and longest exposureperiods. TABLE 6 Second Step Cure Time (min.) and Elastomer Peak LoadTemperature (° C.) Composition (lbs./in²)  40 minutes/204° C. E24 564 40 minutes/204° C. E25 480  40 minutes/215° C. E24 654  40 minutes/215°C. E25 403  60 minutes/193° C. E24 774  60 minutes/193° C. E25 695 170minutes/174° C. E24 1020 170 minutes/174° C. E25 777 170 minutes/174°C., followed by 30 minutes/ E24 987 204° C. 170 minutes/174° C.,followed by 30 minutes/ E25 945 204° C.Illustration E

The results provided in Tables 7 and 8 illustrate examples of a widerange of single elastomers and elastomer blends that may be utilizedwith favorable results in the practice of the present inventionaccording to embodiments thereof. As one skilled in the relevant artwould readily appreciate, various elastomers or blends of elastomers arecommonly used to impart in the vulcanized rubber various combinations ofproperties not readily achievable with a single elastomer, or to enhancecertain properties, e.g., low temperature performance or improveddamping characteristics. In general, these as well as any other suitableand/or conventional elastomers could also be used individually or incombinations of two or more thereof in the practice of the subjectinvention if compounded with appropriate levels ofrubber-to-metal-adhesive coagents and curatives as described above. Forthe examples set forth in Tables 7 and 8 except examples number E61-E63,the first step cure conditions were four minutes at 160° C. followed byexposure of the partially cured elastomer to forty minutes at an appliedtemperature of 204° C., to achieve in each instance an elastomertemperature of about 190° C. for at least 10 minutes. For examplesnumber E61, E62 and E63, the first step cure conditions were fourminutes at 150° C., and the second step cure conditions were sixtyminutes at 193° C., to substantially cure the elastomer composition asabove. As noted above, the first step cure was performed in each case inthe shape-forming mold with the uncured elastomer in contact withneither metal slab, and the second step cure was performed with thepartially cured elastomer disposed between the metal slabs. In eachcase, lap shear adhesion analysis as described above was performed andthe results for peak load so achieved are provided in Tables 7 and 8below. As with the compositions set forth in earlier examples, thecompositions set forth in Table 8 comprised as optional constituents theparaffinic plasticizer oils as shown, and further comprised as optionalconstituents up to about 5 phr of zinc oxide, up to 1.5 phr of zincstearate and/or stearic acid, and up to 10 phr of a conventionalantioxidant and/or antiozonant. TABLE 7 E41 E42 E43 E44 E45 E46 E47 E48E49 Keltan 7441A 175 175 175 175 175 175 175 175 175 Exxon Butyl 268 500 0 0 0 0 0 0 0 Vistanex MM L-140 0 50 0 0 0 0 0 0 0 Vamac D 0 0 50 0 00 0 0 0 Hypalon 40S 0 0 0 50 0 0 0 0 0 Tyrin CM 0 0 0 0 50 0 0 0 0Kraton G1652 0 0 0 0 0 50 0 0 0 Kraton D1112P 0 0 0 0 0 0 50 0 0 KratonD1107 0 0 0 0 0 0 0 50 0 Sterling XC-72 90 90 90 90 90 45 45 45 90 N550Black 0 0 0 0 0 75 75 75 0 Cumar LX-509 0 0 0 0 0 30 15 15 0 Sunpar 22800 0 50 50 50 60 60 60 15 Saret 634 30 30 30 30 30 30 30 30 30 HVA-2 1 11 1 1 1.5 1.5 1.5 1 Varox 231XL 1.8 1.8 1.8 1.8 1.8 3 3 3 5.4 Varox130XL 7.5 7.5 7.5 7.5 7.5 5 5 5 1 Peak Load (lbs./in²) 380 212 437 618479 336 346 332 440

TABLE 8 E57 E58 E51 E52 E53 E55 EVM/ ECO/ E51 E60 E61 E62 E63 EAM EAMEVM EVM EPDM EPDM ECO ECO SBR HNBR NR Vamac D¹ 100 0 0 0 0 0 0 0 0 0 0Vamac HVG² 0 100 0 0 0 0 0 0 0 0 0 Levapren 700 0 0 100 0 0 0 0 0 0 0 0HV³ Levapren 500 0 0 0 100 50 0 0 0 0 0 0 HV⁴ Hydrin 1100⁵ 0 0 0 0 0 0100 50 0 0 0 Hydrin H-55⁶ 0 0 0 0 0 50 0 0 0 0 0 Royalene 580 0 0 0 0 5050 0 50 0 0 0 COPO 1721⁷ 0 0 0 0 0 0 0 0 137.5 0 0 SMR-10⁸ 0 0 0 0 0 0 00 0 0 100 Zetpol 2020⁹ 0 0 0 0 0 0 0 0 0 100 0 N472 0 0 40 40 40 0 0 0 00 0 N293 40 40 0 0 0 0 0 0 0 0 0 N550 0 0 0 0 0 40 40 40 35 40 35Plasthall 7050 0 0 0 0 0 0 10 0 0 0 0 Sunpar 150 0 0 10 10 10 0 0 0 0 00 Ricobond 1756 30 0 0 0 0 0 0 0 0 0 0 HS Saret 633 0 0 0 0 0 0 0 0 0 200 Saret 634 0 15 30 30 30 20 20 20 20 0 25 HVA-2 2 2 0 0 0 0 0 1 0 0 0Vul-Cup 40KE 0 0 0 0 0 0 0 0 4 1.5 1.5 Varox 231XL 5 5 5 5 5 2.1 2.1 4 04 4 Varox 130XL 1 1 1 1 1 0.42 0.42 0.8 0 0 0 Peak Load 162 463 418 391376 317 376 254 77 78 84 (lbs/in²)^(1,2)EAM available under that designation by DuPont Chemical^(3,4)EVM available under that designation by Bayer AG^(5,6)ECO under that designation by Zeon Chemical⁷SBR available under that designation by DSM Copolymer.⁸NR available under that designation by Akrochem⁹HNBR available under that designation by Zeon Chemical.Illustration F

The effects of bonding respective elastomer compositions to differenttypes of metal, in this case, to steel and to aluminum, in accordancewith an embodiment of the present invention are illustrated in Table 9.Uncured elastomer compositions were prepared utilizing the respectiveconstituents set forth in the Table 9 as described above, and elastomerslabs as described above for Lap Shear adhesion analysis were formedtherefrom by compression molding individual specimens in appropriatelydimensioned compression molds under first stage curing conditions of 4minutes at 160° C. The respective surfaces of these partially curedelastomer slabs were then wiped with isopropyl alcohol in accordancewith conventional rubber preparation methods. For each composition notedbelow, thus-prepared elastomer slabs were then applied between two steeltest slabs and also between two aluminum slabs, each having thedimensions noted above for Lap Shear adhesion analysis metal slabs,utilizing P80 lubricating oil applied to the metal surface, and under anapplied force resulting in 25% compression of the rubber. Theseassemblies were each allowed to sit for 4 hours, and then exposed in ahot air oven to an applied temperature of 204° C. for 40 minutes tosubstantially fully cure the elastomer composition and accomplish thesecond stage cure. Lap Shear adhesion analysis in accordance with ASTMD816 as described above was then performed both at room temperature andat 100° C., with a pull rate of 0.5 inches per minute, and both the peakload achieved prior to failure and the percent rubber coverage wererecorded. Percent rubber coverage indicates the level of cohesive versusadhesive failure that occurred for the test specimens.

The results set forth in Table 9 indicate excellent adhesion of allspecimens to steel under both room temperature and elevatedtemperatures, and similarly reveal some degree of adhesion to aluminum.Notably, the compositions set forth in Table 10 were designed foradhesion to steel surfaces, and optimization of the respectivecompositions' adhesion to aluminum was not attempted for thisillustration. The practitioner having ordinary skill in the relevant artwould readily appreciate however that adhesion of comparable elastomercompositions to aluminum or any other metal could be optimized withinthe scope of the present invention according to known methods, such asby altering one or more composition constituents or their relativeamounts in the composition, e.g., adhesive adjuvant and/or curative.TABLE 9 E64 E65 E66 E67 E68 E69 E70 E71 E72 Compound Ingredients Keltan7441A 175 175 175 175 175 175 175 175 175 N472 40 50 50 50 50 50 88 4040 N550 80 70 70 70 70 70 0 80 50 FRANKLIN T-14 0 50 0 0 0 0 0 0 0 DIXIE2.6 0 0 50 0 0 0 0 0 0 MISTRON VAPOR 0 0 0 50 0 0 0 0 0 MCNAMEE CLAY 0 00 0 50 0 0 0 0 SUNPAR 2280 60 60 60 60 60 60 20 60 50 SARET SR-634 30 3030 30 30 30 30 30 30 HVA-2 1.5 1.5 1.5 1.5 1.5 1.5 1 1.5 2 VAROX 130XL 55 5 5 5 5 7.5 3.2 5 VAROX 231XL 3 3 3 3 3 3 1.8 5 5 Adhesion Results-Peak Load (lbs./in²), 20° C., on Steel 580 476 368 479 310 488 741 307236 % rubber coverage, 20° C., on Steel 25 50 10 100 5 15 80 5 5 PeakLoad (lbs./in²), 100° C., on Steel 371 365 286 243 270 306 321 107 102 %rubber coverage, 100° C., on Steel 75 100 75 95 75 100 75 20 10 PeakLoad (lbs./in²)), 20° C., on Aluminum 189 278 214 299 189 269 259 99 114% rubber coverage, 20° C., on Aluminum 0 0 0 2 0 0 0 0 0 Peak Load(lbs./in²), 100° C., on Aluminum 87 201 103 215 99 173 111 40 49 %rubber coverage, 100° C., on Aluminum 0 10 2 80 0 5 0 0 0Illustration G

Effects of the presence of conventional rubber-to-metal assembly surfacecontaminants on the relevant metal surface are illustrated in Table 10.The contaminants listed in Table 10 are representative of common oils,lubricants and machining coolants conventionally employed in theassembly of rubber-to-metal bonded parts, exemplified by automotivecrankshaft torsional vibration dampers. In each case, uncured elastomerspecimens were prepared in accordance with the rubber mixing protocolset forth above, and Lap Shear adhesion analysis slabs were then formedvia injection molding techniques, with a first cure of 165° C. for anexposure period of 2 minutes. In each case, the respective steel slabswere coated with a thin film of the noted contaminant. Thereafter, thepartially cured elastomer slabs were introduced between the treatedsteel slabs, the assemblies allowed to stand for approximately 4 hours,and then the assemblies were cured in a second cure stage performed atand applied temperature of 204° C. for and exposure period of 40 minutesto substantially fully cure the elastomer composition. The so formed LapShear adhesion analysis specimens were then pulled in accordance withASTM D816 as described above, at a rate of 0.5 inches per minute.

As indicated above, it is generally accepted in the art thatrubber-to-metal bonding utilizing an adhesive at the rubber-to-metalinterface requires extensive and thus costly preparation of the metalsurface. In general, the metal must be clean, free of any oils,lubricants and other contaminants. The results provided in Table 10indicate however that adhesion of rubber to metal in accordance with anembodiment of the subject invention is much more flexible and forgiving.Surprisingly, it has been found that better adhesion results when therubber is held in contact with the contaminant-coated metal for asufficient amount of time to allow the contaminant to soak at leastpartially into the rubber, e.g., from about 1 to 4 hours. TABLE 10 PeakLoad Contaminant: Rubber (lbs./in²) Harmony AW-46, a clean hydraulic oilE24 872 ″ E25 617 Ultima EP-220, a clean gearbox oil E24 764 ″ E25 636Dascoway 68, a clean Waylube oil E24 767 ″ E25 376 Drawsol 165 M, aclean draw compound E24 453 ″ E25 748 S500-US, 5% in water, a cleancoolant E24 587 ″ E25 531 Used coolant, about a week old E24 626 ″ E25700 Used coolant, about two weeks old E24 487 ″ E25 560As indicated above, the present invention is not intended to be limitedto the practice of crankshaft torsional vibration dampers, but isinstead applicable to any construction in which rubber-second substrateor rubber-to-metal bonding applies. Thus for example, in theconstruction of rolls, such as may be utilized in conjunction with theoperation of printing presses or copy machines for instance, the subjectinvention would similarly provide improved production flexibility asdescribed above. According to conventional practice, rolls areindividually assembled by first applying a rubber-to-metal adhesive to ametal shaft, and then in a single curing step, vulcanization bondinguncured elastomer to the prepared shaft, generally within a suitablyshaped mold to form the final vulcanized rubber profile. This process iscostly in that rolls must be assembled individually, each through aseparate rubber molding process. In accordance with the subjectinvention however, it is anticipated that one could instead prepare viaconventional rubber molding processes, e.g., extrusion molding, a lengthor tube of partially cured elastomer having the appropriatecross-sectional dimensions. A first cure stage, sufficient to partiallycure the elastomer to a point at which it could be handled ormanipulated for storage and/or further production purposes withoutadverse impact on the dimensional integrity of the piece, could beimparted in the molding process itself. Subsequently the partially curedelastomer tube could be cut to an appropriate length for bonding in asubsequent second cure stage to the relevant metal shaft. Again,excellent rubber-to-metal adhesion could be accomplished utilizing suchprocess in accordance with the present invention, and the need for aseparate adhesive at the rubber-to-metal adhesive would be eliminated.Moreover, any slight rubber shrinkage that may occur during the secondcure stage would provide additional force to hold the rubber in placeagainst the metal shaft.

In further non-limiting examples of embodiments of the presentinvention, the two-step cure process described above could be utilizedwith advantage in adhering the relevant rubber member to thecorresponding metal or plastic reinforcement member in the constructionof bonded rubber articles such as reinforced hose and transmission beltssuch as flat belts, toothed- or synchronous belts, V-belts andmulti-v-ribbed belts. Non-limiting examples of synchronous belts forforming same are disclosed in aforementioned U.S. Pat. No. 2,507,852 toCase; U.S. Pat. No. 3,250,653 to Geist et al. and U.S. Pat. No.3,078,206 to Skura, the contents of which with regard to such processesis incorporated herein by reference.

In each such case, the relevant rubber member could be bonded to therelevant substrate, e.g., the metal or plastic or textile reinforcementmember of a hose, or the metal or synthetic tensile member of the belt,by curing the rubber member in two stages, wherein at least the secondcure step would be performed with the partially cured rubber in contactwith the surface of such relevant substrate. In each case theutilization of the method in accordance with an embodiment of thepresent invention would provide the possibility of eliminating anadhesive or other intervening coating at the relevant rubber:substrateinterface while providing improved process- or production flexibility asdescribed above. Moreover it is contemplated that in the construction ofsynchronous belts, e.g., by the tooth preform method described inaforementioned U.S. Pat. No. 3,250,653 or the flow-through methoddescribed in aforementioned U.S. Pat. No. 3,078,206, utilization of themethod in accordance with an embodiment of the present invention couldprovide improved control over the tensile cord position during the beltbuilding process. This in turn would likely improve pitch fitconsistency in production. One could for example partially cure anelastomer coating applied to the surface of the belt tensile cord orreinforcing fabric in a first cure step, thereby providing improveddimensional stability to the cord, then apply the so-formed assembly tothe balance of the belt component parts in accordance with theadditional belt building steps provided in e.g., the pre-form orflow-through method, and then complete the cure of the coating in asecond cure step in order to bond the tensile cord or reinforcing fabricto the surrounding belt constituent members.

In general, the present invention provides in embodiments thereof aprocess for chemically bonding rubber to a second surface including ametal surface, and a bonded I part formed thereby, which allows for theelimination of an adhesive application at the relevant interface, and,according to one embodiment, provides improved production flexibilitycompared to conventional methods, while offering the practitioner thepossibility of varying performance properties and elastomercharacteristics as desired for a given application. Thus for example,two cure stages can be accomplished by controlling cure time andtemperature utilizing a single curative or cure system, or canalternatively be accomplished utilizing two separate curatives, eachbeing activated at a different stage such as by controlling exposuretemperature. The concentration of two curatives within a singlecomposition can moreover be varied over a wide range while maintaining avery high level of adhesion to substrates including metal, withgenerally predictable effects on rubber processing and physicalproperties. Thus for example, the amount of a first peroxide curativecan be optimized to yield very high tear strength for ease ofpartially-cured rubber demolding. The amount of a second peroxidecurative can moreover be optimized for low compression set in thefinished part. While as noted above the present invention provides theability to durably bond rubber to, e.g., a metal substrate, in theabsence of a separate adhesive or other coating layer, the absence ofsuch layer or composition at the relevant rubber:metal orrubber:substrate surface is not necessary in the practice of the presentinvention.

Although the present invention has been described in detail for thepurpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by oneskilled in the art without departing from the spirit or scope of thepresent invention except as it may be limited by the appended claims.The invention disclosed herein may suitably be practiced in the absenceof any element not specifically disclosed herein.

1. A process for forming a bonded part comprising a rubber member and atleast one of a first outer member and a second outer member, comprisingthe steps of: a. placing an uncured elastomer composition comprising atleast one elastomer, at least one adhesive adjuvant and at least onecurative into a shape-forming mold; and characterized in that theprocess further comprises the steps of: b. exposing said elastomercomposition to a first cure step comprising at least one of a firsttemperature and a first pressure over a first exposure period sufficientto less than fully cure said elastomer composition; c. placing the soformed less than fully cured elastomer composition in contact with asurface of at least one of said first outer member and said second outermember; and d. exposing said less than fully cured elastomer compositionto a second cure step comprising at least one of a second temperatureand a second pressure over a second exposure period sufficient tosubstantially fully cure said elastomer composition.
 2. The process ofclaim 1 wherein at least one of said first- and said second members isformed of metal, and wherein said adhesive adjuvant is a rubber-to-metaladhesive adjuvant.
 3. The process of claim 1 wherein said less thanfully cured elastomer composition is in direct contact with said surfaceof said outer member.
 4. The process of claim 1 further comprising thestep of removing said less than fully cured elastomer composition fromsaid shape-forming mold prior to said second cure step.
 5. The processof claim 2 wherein said at least one rubber-to-metal adhesive adjuvantis one selected from the group consisting of Type I coagent compounds,Type II coagent compounds, tackifiers, and a combination of at least anytwo of the foregoing.
 6. The process of claim 2 wherein said at leastone rubber-to-metal adhesive adjuvant is at least one selected from thegroup consisting of; a. a metal salt of an alpha-beta unsaturatedorganic acid, b. a bis-maleimide, and c. a maleated polybutadiene resin.7. The process of claim 1 wherein said at least one elastomer isselected from the group consisting of ethylene-alpha-olefin elastomer,ethylene/acrylic elastomer, polychloroprene rubber, acrylonitrilebutadiene rubber, hydrogenated acrylonitrile butadiene rubber,styrene-butadiene rubber, alkylated chlorosulfonated polyethylene,epichlorohydrin, polybutadiene rubber, natural rubber, chlorinatedpolyethylene, brominated polymethylstyrene-butene copolymers, siliconerubber, styrene-butadiene-styrene block copolymer,styrene-ethylene-butadiene-styrene block copolymer, acrylic rubber,ethylene vinyl acetate elastomer, and a combination of two or more ofthe foregoing.
 8. The process of claim 1 wherein said at least onecurative is selected from the group consisting of a free-radicalproducing agent; sulfur; a sulfur-cure accelerator; an amine; and acombination of two or more of the foregoing.
 9. The process of claim 1wherein said bonded part comprises said first outer member and saidsecond outer member, and said less than fully cured elastomercomposition is placed between said outer members.
 10. The process ofclaim 9 further comprising the step of compressing said less than fullycured elastomer composition between said first outer member and saidsecond outer member prior to exposing said less than fully curedelastomer composition to said second cure step, such that said less thanfully cured elastomer composition is disposed under compression betweensaid first and second outer members.
 11. The process of claim 9 furthercomprising the step of placing said uncured elastomer composition incontact with a surface of one of said first outer substrate and saidsecond outer substrate.
 12. The process of claim 1 wherein said bondedpart is selected from a torsional vibration damper, a rubber-viscousvibration isolation damper, a vibration isolator, a vibration isolationmount, a vibration damper, a coupling, a rubber roll, a transmissionbelt and a hose.
 13. A process for forming a torsional vibration dampercomprising a cured elastomer composition, a first metal surface and asecond metal surface, comprising the steps of: a. placing an uncuredelastomer composition comprising at least one elastomer, at least onecurative, and at least one rubber-to-metal adhesive adjuvant into ashape-forming mold; b. exposing said uncured elastomer composition to afirst pressure and a first applied temperature over a first exposureperiod sufficient to only partially cure the composition to a state ofcure of from about 20% to about 99% as determined in accordance withASTM D5289; c. disposing said partially cured elastomer compositionbetween said first metal surface and said second metal surface; and d.exposing said partially cured elastomer composition to at least one of asecond pressure and a second applied temperature over a second exposureperiod sufficient to substantially fully cure said elastomercomposition.
 14. The process of claim 13 wherein said first pressure,said first applied temperature and said first exposure period aresufficient to cure the composition to a state of cure of from about 50%to about 95% as determined in accordance with ASTM D5289.
 15. Theprocess of claim 13 wherein said first pressure, said first appliedtemperature and said first exposure period are sufficient to cure thecomposition to a state of cure in the range of from about 70% to about90% as determined in accordance with ASTM D5289.
 16. The process ofclaim 13 further comprising the step of incorporating in said elastomercomposition a first curative and a second curative, said first curativeexhibiting a first activation temperature and said second curativeexhibiting a second activation temperature; and wherein said firstapplied temperature and time is sufficient to activate said firstcurative, and said second applied temperature and time is sufficient toactivate said second curative.
 17. The process of claim 13 furthercomprising the step of compressing said less than fully cured elastomercomposition between said first outer member and said second outer memberprior to exposing said less than fully cured elastomer composition tosaid second cure step, such that said less than fully cured elastomercomposition is disposed under compression between said first and secondouter members.
 18. The process of claim 13 further comprising the stepof exerting force onto said subassembly to achieve a compression of saidelastomeric composition of up to about 50% prior to said second curingstep.